mcp-mat

Headless MCP server for Eclipse MAT using direct java -jar org.eclipse.equinox.launcher_*.jar execution.

Features

• mat_healthcheck — Validate MAT launcher and Java runtime availability

• mat_parse_report — Run predefined MAT reports (leak suspects, system overview, etc.)

• mat_oql_query — Execute OQL queries and return inline results

• mat_run_command — Execute 56 built-in MAT analysis commands (histogram, dominator_tree, path2gc, thread_overview, etc.)

• mat_index_status — Check whether MAT index artifacts exist for a heap dump

• mat_oql_spec — Return OQL parser guidance and supported patterns

Related MCP server: heap-seance

Supported Commands (mat_run_command)

Dominator tree analysis

dominator_tree, show_dominator_tree, immediate_dominators, big_drops_in_dominator_tree

Path to GC roots

path2gc, merge_shortest_paths, gc_roots

Histogram & object listing

histogram, delta_histogram*, list_objects, group_by_value, duplicate_classes

Leak detection

leakhunter, leakhunter2, find_leaks, find_leaks2, reference_leak

Thread analysis

thread_overview, thread_details, thread_stack

Collection analysis

collection_fill_ratio, collections_grouped_by_size, array_fill_ratio, arrays_grouped_by_size, hash_entries, map_collision_ratio, extract_list_values, hash_set_values, primitive_arrays_with_a_constant_value

Reference analysis

references_statistics, weak_references_statistics, soft_references_statistics, phantom_references_statistics, finalizer_references_statistics

Finalizer analysis

finalizer_overview, finalizer_thread, finalizer_queue, finalizer_in_processing, finalizer_thread_locals

Retained set

show_retained_set, customized_retained_set

Component & top consumers

component_report, component_report_top, top_consumers, top_consumers_html, pie_biggest_objects

String & memory waste

find_strings, waste_in_char_arrays

Heap info & misc

heap_dump_overview, unreachable_objects, system_properties, class_references, comparison_report*

Eclipse/OSGi specific

bundle_registry, leaking_bundles

Export

export_hprof

* Requires a baseline heap dump (second .hprof file).

OQL mode notes

• This server normalizes client OQL input and wraps it for MAT parse-app command mode.

• You can send OQL with or without outer quotes.

• For class ranking and top consumers, prefer mat_parse_report with org.eclipse.mat.api:overview and parse Class_Histogram*.txt.

• For object inspection, use simple field-level OQL patterns (INSTANCEOF, OBJECTS 0x...).

Environment

All environment variables are optional:

• MAT_HOME

• MAT_LAUNCHER

• JAVA_PATH (default java)

• MAT_XMX_MB (default 4096)

• MAT_TIMEOUT_SEC (default 1800)

• MAT_CONFIG_DIR (default /tmp/mat-config)

• MAT_DATA_DIR (default /tmp/mat-workspace)

• MAT_DEBUG (default false)

• MAT_DEBUG_LOG_DIR (default /tmp/mcp-mat-logs)

• MAT_PRIVACY_MODE (default false)

• MAT_OQL_MAX_BYTES (default 16384)

• MAT_RESULT_PREVIEW_LINES (default 20)

• MAT_STDIO_TAIL_CHARS (default 4000)

Run

npm install
npm run build
MAT_HOME=/path/to/mat node dist/src/server.js

Test

npm test

Install via npx

No build step required. Install directly from npm:

Claude Code

Add to ~/.claude/settings.json or project .claude/settings.json:

{
  "mcpServers": {
    "mat": {
      "command": "npx",
      "args": ["-y", "mcp-mat"],
      "env": {
        "MAT_HOME": "/Applications/MemoryAnalyzer.app/Contents/Eclipse"
      }
    }
  }
}

Codex

codex mcp add \
  --env MAT_HOME=/Applications/MemoryAnalyzer.app/Contents/Eclipse \
  mat \
  npx -y mcp-mat

Install in Claude Code (from source)

Add the MCP server to Claude Code settings (~/.claude/settings.json or project .claude/settings.json):

{
  "mcpServers": {
    "mat": {
      "command": "node",
      "args": ["/path/to/mcp-mat/dist/src/server.js"],
      "env": {
        "MAT_HOME": "/Applications/MemoryAnalyzer.app/Contents/Eclipse"
      }
    }
  }
}

Install in Codex (from source)

Build first:

cd /path/to/mcp-mat
npm install
npm run build

Add MCP server to Codex:

codex mcp add \
  --env MAT_HOME=/Applications/MemoryAnalyzer.app/Contents/Eclipse \
  mat \
  node /path/to/mcp-mat/dist/src/server.js

Verify:

codex mcp list
codex mcp get mat --json

If you need to update the entry:

codex mcp remove mat
# then run codex mcp add ... again

Equivalent ~/.codex/config.toml entry:

[mcp_servers.mat]
command = "node"
args = ["/path/to/mcp-mat/dist/src/server.js"]

[mcp_servers.mat.env]
MAT_HOME = "/Applications/MemoryAnalyzer.app/Contents/Eclipse"